Generally, a bicycle, a wheelchair, a handcart or the like, which has wheels and travels using various kinds of driving forces such as man power or an electromotive force, is provided with a transmission for changing a traveling speed.
Such a transmission performs shifting in multiple stages from a high speed to a low speed according to manipulation of a rider or user to obtain torque or speed required under a traveling condition.
In particular, recently, a planetary gear set consisting of a sun gear, planetary gears, a ring gear and a carrier is provided in a hub shell to achieve a compact configuration, thereby performing shifting in multiple stages and preventing the gears from being exposed to the outside.
However, there are technical problems in that a conventional multi-stage transmission using a planetary gear set has a small number of shifting stages in spite of a complicated structure, and in particular, a pawl that has been engaged with an inner peripheral surface of the sun gear to restrict rotation of the sun gear is not disengaged during shifting manipulation, resulting in unsmooth shifting.